Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.86	8.371%	$99.5496	$99.55	$99.55	$99.50
Purchase #2	$163.93	11.543%	$182.8524	$182.85	$182.85	$182.90
Purchase #3	$62.98	6.835%	$67.2847	$67.28	$67.30	$67.30
Purchase #4	$37.33	4.792%	$39.1189	$39.12	$39.10	$39.10
Purchase #5	$31.64	13.435%	$35.8908	$35.89	$35.90	$35.90
Purchase #6	$247.72	10.496%	$273.7207	$273.72	$273.70	$273.70
Purchase #7	$21.58	5.210%	$22.7043	$22.70	$22.70	$22.70
7 purchase totals =	$657.04		$721.1214	$721.11	$721.10	$721.10